1. Field of the Invention
The present invention relates, in general, to the manufacture of integrated circuits. More particularly, the present invention provides a photoresist copolymer for deep ultra violet (hereinafter referred to as "DUV") light and a method for preparing the same. The photoresist copolymer, which is useful for easily forming the fine patterns allowable for the high integration of semiconductor devices by a microlithography process using DUV light.
2. Description of the Prior Art
Certainly, the recent burst into the high integration of semiconductor devices is greatly dependent on advances in microlithography. In this regard, DUV such as Krf or ArF, is developed as a light source, requiring novel photoresists. Now, chemical amplification type photoresists are prevailingly used for DUV light.
Typically, such a chemical amplification type photoresist for DUV light comprises a polymer, a solvent a photoacid generator and other additives.
In order to employ ArF as a light source, the polymer of photoresist is of eligibility for many aspects, including, for example, transparency to Arf light, etch resistance, developability in 2.38% tetramethyl ammonium hydroxide (TMAH) and adhesiveness.
It is, however, difficult to synthesize the polymer having all of such properties. For example, resins having polyacrylate as a main chain are easy to synthesize but are poor in etch resistance and development. The etch resistance can be improved by introducing alicyclic units into the main chain. A chain whose backbone consists of alicyclic units alone is very difficult to obtain.
Another example is a conventional photoresist comprises an alicyclic polymer represented by the following chemical formula I: ##STR1## wherein, x, y and z each represents a polymerization degree ranging from 0 to 99.9. In Formula I, "A" moiety, anhydride, is used to polymerize alicyclic olefin group. This anhydride moiety, however, is very soluble to 2.38% TMAH although it is not exposed to light. The solubility problem of the anhydride can be overcome by increasing the y ratio, that is, by increasing the fraction of tertiary butyl. Correspondingly, the z ratio is reduced. Since the adhesiveness of the photoresist is often dependent on this ratio, the resulting photoresist is disadvantageously released from the wafer upon patterning.
In order to overcome drawback of Formula I, a two-component system was developed in which a cholesterol compound is used as a dissolution inhibitor at an amount of about 30% of photoresist resin. However, such a molecular structure containing dissolution inhibitor as mentioned above, is basically impossible to use in photoresist.
The aforementioned conventional techniques allow an easy polymerization of alicyclic olefins but the resulting copolymers are not stable in molecular structure so that they are not suitable for use as photoresist resins. In turn, the photoresists of the conventional techniques give the patterning process for semiconductor devices difficulty, deleteriously affecting the properties and reliability of the semiconductor devices produced. Consequently, the high integration of semiconductor devices is difficult with the above conventional techniques.